WSL1 was like that, but it was severely handicapped by NT filesystem performance, especially for small files or metadata operations. There are a lot of small operations that are more than 2 orders of magnitude slower on Windows than on Linux, and a lot of Linux software just expects them to be fast, so WSL1 is not a great experience for a lot of stuff.
This seems to be a known issue, but nobody knows how to fix it. (It's some UAC thing, apparently.) I imagine this is what WSL 1 used, and it was similarly slow.
From the original NT microkernel design, filesystem access is all asynchronous messaging, and it can be intercepted and modified by drivers at many points. A lot of software takes advantage of that. But it's also why caching isn't as effective as it could be, since you can't rely on all those unknown layers returning the same result each time.
Plus a lot of Windows systems are running an AV which likes to check to see if you should be allowed to read any particular file in case it might be dangerous.
In relation to the above conversation about WSL1 performance characteristics, my impression is that ReFS would be equal or worse to NTFS for what Linux/POSIX file operations expect. (ReFS is still very much on the "SQL Database" side of the analogy, like NTFS as it was of course designed to support much the same transactional semantics, and some additional ones as well at the "virtual storage space" level above the physical pool of drives.)
In danger of getting further aside into tangential spaces, Ubuntu's current experimentation with ZFS by default is probably one to watch to see if the user experience of complicated multi-physical disk file systems like ReFS can be made to fit and is useful to a broader user base than just power users. (Though arguably compared to the broader spectrum of casual Windows users, even some of the more casual Ubuntu users might be considered power users in comparison.)
And no matter how much MS improves WSL 1 there would always be something missing that enough users want/need. For example I care more about the network related stuff that wasn't implemented (NETLINK_ROUTE\RTM_GETROUTE, AF_PACKET family) because this excluded nmap.
I think Docker on Windows also uses it but I don't use that. Windows Defender has never indicated a requirement for Hyper-V to me.
Also they said "That doesn't mean we've given up either", but you really have to do some mental gymnastics to convince yourself that moving to a VM wasn't "giving up" on solving these problems in WSL1.
But in any case, I think the component you want to refer to in that case it the "I/O subsystem".